DESCRIPTION: The applicant proposes experiments along several lines, all ultimately directed towards a better understanding of the cell biology of photoreceptor cells, both in vertebrates and invertebrates. In vertebrate photoreceptors, three specific aims will be pursued: (1) to further understand the mechanisms of bleaching adaptation, the longitudinal spread of the effects of bleaching desensitization will be determined and the effects of 11-cis-locked analogs and light polarization on these phenomena will be explored; (2) to understand the mechanisms that may account for limited spread between inner and outer segment of integral plasma membrane proteins, the lateral diffusion of lipid soluble fluorescent probes restricted to the plasma membrane will be quantitated; and (3) to understand the control of respiration in photoreceptor mitochondria, the O2 consumption in isolated rods will be measured and the regulation of this consumption by light and cytoplasmic molecules such as Ca, ATP and ADP will be examined. In studies of invertebrate photoreceptors, under aim 4, the effects of IP5 on light- sensitive voltages and the control of Ca cytoplasmic concentration will be determined.